Stationary and transport applications of air conditioning and transport refrigeration systems control the temperature of a conditioned space to a predetermined temperature range adjacent to a predetermined set point temperature, with transport applications including those used with straight trucks, tractor-trailer combinations, refrigerated containers, and the like. Such air conditioning and refrigeration systems conventionally utilize a chlorofluorocarbon (CFC) refrigerant in a mechanical refrigeration cycle. The mechanical refrigeration cycle requires a refrigerant compressor driven by a prime mover, which often includes an internal combustion engine, such as a diesel engine. Because of the suspected depleting effect of CFC's on stratospheric ozone (O.sub.3), practical alternatives to the use of CFC's in air conditioning and refrigeration systems are being sought.
The use of a cryogen, i.e., a gas which has been compressed to a very cold liquid state, such as carbon dioxide (CO.sub.2) and nitrogen (N.sub.2), in air conditioning and refrigeration systems is particularly attractive because, in addition to eliminating the need for a CFC, it also eliminates the need for a compressor and associated prime mover.
Thus, it would be desirable, and it is an object of the present invention, to provide reliable, practical methods and apparatus which utilize a cryogen in air conditioning and refrigeration systems.